Significance The sperm peptide PH-20 was evaluated as a potential immunocontraceptive vaccine by immunizing animals, then breeding to determine the actual contraceptive effectiveness. The development of a contraceptive vaccine could be useful for populations in developing countries where access to medical care is limited. Objectives Adult female cynomolgus macaques in treatment and control groups received five separate treatments. The treatment group received 100 5g cPH-20 plus 10 5g cholera toxin (CT) in 1.0 ml phosphate buffered saline (PBS); the control group received 10 5g CT in 1.0 ml PBS. Blood was collected on study days 49 and 79 and vaginal lavage performed on study day 31 for control group and study day 33 for treatment group, and on study day 42 for both groups. Animals were bred on cycle days 6, 8, 10, 12 and 14 of their menstrual cycle after study day 45, for a total of four cycles or until confirmed pregnancy. Results In this first cycle of breeding, nine control animals were bred and all had positive coital tests, and nine treatment animals bred, seven having positive coital tests. Out of the three remaining control animals, two have been re-bred and pregnancy results are pending. The remaining control group animal not bred, has not cycled since August 15, 1997. In the treatment group, the tenth animal has been scheduled for its first cycle of breeding, and the other four negative animals have been re-bred. Of these four treatment animals bred during cycle two, one has been confirmed as positive, two negative and one pending results respectively, bringing the total treatment group pregnancies to six. Future Directions Additional work on the PH-20 protein will be conducted prior to next study in hope of improving length of effectiveness of vaccine. KEYWORDS immuno-contraception, sperm antigens, vaccine